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    <title>Document</title>
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<body>
    <script>
        // 写出闰年的条件
        var year = prompt("请输入年份：");
        // 1、年份能被4整除，但不能被100整除
        // 2、年份能被400整除
        alert((year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0));
    </script>
</body>
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